1. Field of the Invention
The present invention relates to an electronic distribution type ignition apparatus for internal combustion engine for controlling the feed and shut-oil of a primary current i1 to and from an ignition coil using a power transistor 14, and more specifically, to an ignition apparatus for internal combustion engine by which malfunction caused when the primary current i1 starts to be fed (at the rising-up of an ignition signal) can be effectively prevented without using a high-tension diode.
2. Description of the Related Art
Conventionally, an electronic distribution type ignition apparatus for internal combustion engine having an independent ignition coil for each ignition plug controls an amount of fuel to be injected into each cylinder and an ignition timing by electronic calculation using a microcomputer.
At the time, although a primary current i1 is fed to and shut off from the ignition coil by turning on and off a power transistor 14 in response to an ignition signal, there is a possibility that malfunction such as advanced ignition and the like is caused because a high-tension secondary voltage V2 is induced when the ignition signal rises up.
To prevent the above malfunction, the conventional ignition apparatus for internal combustion engine inserts a high-tension diode to the secondary side of the ignition coil to prohibit the output of the high-tension secondary voltage when the ignition signal rises up.
The conventional ignition apparatus for internal combustion engine will be described below with reference to FIG. 11 and FIG. 12. FIG. 11 is a circuit arrangement diagram showing the conventional ignition apparatus for internal combustion engine and FIG. 12 is a waveform diagram explanatory of operation of the conventional apparatus shown in FIG. 11.
In FIG. 11, an ignition power unit 1 includes an ignition coil 13 composed of a primary coil 11 and a secondary coil 12 and a power transistor 14 for feeding and shutting off a primary current i1 to and from the primary coil 11 and applies a high-tension secondary voltage V2 output from the secondary coil 12 to the ignition plug 3 of each cylinder.
A malfunction preventing high-tension diode 15 is inserted to the output terminal of the secondary coil 12 to cut a positive polarity voltage superposed with the secondary voltage V2. The primary coil 11 and secondary coil 12 in the ignition coil 13 has a common distribution terminal connected to a battery power unit.
The power transistor 14 is composed of an emitter-grounded NPN transistor with its collector connected to the primary coil 11.
A control circuit 2 includes a CPU 21 composed of a microcomputer and an output transistor 22 for amplifying a control signal from the CPU 21. The CPU 21 controls fuel injection to each cylinder of an internal combustion engine in response to an operating state signal D from various sensors (not shown) as well as calculates an ignition timing (corresponding to the shut-off timing of the primary current i1) and a feeding time of the primary current i1 (corresponding to the pulse width of the ignition signal G) to output the ignition signal G to the power transistor 14 through the output transistor 22.
The output transistor 22 is composed of an emitter-grounded NPN transistor with its collector connected to the battery power unit.
The ignition signal G is applied to the base of the power transistor 14 to feed and shut off the primary current i1 to generate the high-tension secondary voltage V2 from the ignition coil 13.
The operating state signal D obtained from the various sensors include, for example, an engine r.p.m., amount of intake air, cooling water temperature, intake manifold pressure, throttle opening, depressed amount of an accelerator pedal and the like.
FIG. 12 is a waveform diagram of various signals in FIG. 11 and shows the change in time of the collector potential Vc of the power transistor 14, primary current i1 and secondary voltage V2.
Next, operation of the conventional ignition apparatus for internal combustion engine shown in FIG. 11 will be described with reference to FIG. 12.
First, the CPU 21 in the control circuit 2 injects fuel to each cylinder of the internal combustion engine at an optimum timing in response to the operating state signal D as well as outputs the ignition signal G to optimize a period of time for feeding the primary current i1 and an ignition timing (shut-off timing).
The power transistor 14 in the ignition power unit 1 is turned on in response to the ignition signal G of H level to start the feed of the primary current i1 to the primary-coil 11.
The ignition signal G is changed to L level at an optimum timing after the primary current i1 reaches a target current value to thereby turn off the power transistor and shut off the primary current i1. With this operation, the high-tension secondary voltage V2 is induced to the secondary coil 12 so that ignition is carried out by spark discharged from the ignition plug 3.
However, when the collector voltage Vc of the power transistor 14 steeply falls down at the rising-up of the ignition signal G, an induction voltage is generated to the ignition coil 13 and a noise signal of relatively high tension is superposed with the secondary voltage V2 as shown by a dotted line of FIG. 12.
If discharged spark is generated to the ignition plug 3 of a cylinder in an intake stroke or compression stroke by such a noise signal, ignition control will be carried out at an undesired earlier timing.
Consequently, the high-tension diode 15 is inserted to the output terminal of the ignition coil 13 to output the secondary voltage V2 from which the superposition of the positive polarity noise signal is cut as shown by a solid line of FIG. 12.
That is, the high-tension diode 15 prohibits the application of the secondary voltage V2 to the ignition plug 3 when the feed of the primary current i1 is started to thereby prevent the advanced ignition of the ignition plug 3. With this arrangement, malfunction can be prevented by suppressing the influence of the secondary voltage V2 when the primary current i1 starts to be fed.
However, the insertion of the high-tension diode 15 increases the number of parts and the circuit arrangements and thus increases the size and weight of the apparatus due to the need of a space for mounting the parts and an insulation space as well as increases a working cost for the assembly of the ignition coil 13 and connection to the coil 12 and the like.
Further, since the high-tension diode 15 is applied with the high-tension secondary voltage V2 and incorporated in the vicinity of the ignition coil 13 which generates high temperature, the diode 15 must be arranged as a component having sufficiently high reliability to endure an adverse environment in which it is used and thus its cost is increased, by which the cost of the apparatus is increased.
Since the conventional ignition apparatus for internal combustion engine has the high-tension diode 15 inserted to the output terminal of the ignition coil 13 for generating the secondary voltage V2 to prevent malfunction caused when the ignition signal G rises up, the apparatus has a problem that the number of parts is increased and thus the apparatus is increased in size, by which its cost in also increased.